I do have it and have had it since its release. I've really only messed around with it a few times and with friends--but overall just singing some songs just doesnt interest me. But to be fair, I've never played a Singstar before this one so I really have nothing to compare this to--except Rock Band.
In comparison to Rock Band, the singing mechanic appears to be slightly weaker and less fun. You know how RB has the pitch meter, so you can see where you'r voice is registering? This doesnt have that scale at all. This might something that's been in previous versions, sure, but I found it a tad annoying that I had to sing to find out where my pitch was as the song is flying by. Might be petty to some, but I love that kind of feedback--it helps me get better more quickly with the song.
The use of the camera is really cool and a great idea. There was one point where me, my wife and a few friends scrolled through the on-line video browers (depending on the day, there are new videos every minute being uplaoded) to check out other people and we were cracking up at the stuff people uploaded. It was a very wide range of people too. We saw lots of older couples singing and cracking up, groups of younger people just goofing off--it was kind of refreshing in a weird way.
In one instance there were two little kids--a little boy and a younger girl--who were recording a video behind their parents back. The camera caught them chatting about this so we were laughing because we just KNEW they were going to get caught! Nearing the end, the little sister was really starting to giggling a little too hard and she just fell down. She couldnt even finish the song she was laughing so hard. Suddenly daddy enters the room from behind without them noticing, smiling and just folding his arms as he leaned up against the wall. It was pretty adoreable when they saw him. Good times. The video stuff wasnt nearly as annoying as we thought it would be.
The music store has just a TON of videos--too bad they're all in SD.

Let me know if you have any questions and I'll try to answer them.